Written by Scott Schreeg | Power Plants

Reducing noise efficiently is critical for smooth operations in gas turbine power plants. Traditional exhaust silencers, with their parallel baffle setups, have effectively met noise standards amidst the challenges of turbine exhaust. However, with recent advancements, the demand for better insulation methods is apparent. In many cases, upgrading to acoustical pillows for turbine exhaust silencer insulation makes sense.

Traditional Exhaust Silencer Design

Traditionally, a gas turbine power plant would use an absorptive exhaust silencer designed to meet the site’s permitted noise criteria. A typical absorptive silencer design usually consists of a parallel baffle arrangement (see pic) called splitters, panels, or baffles. This silencer design works well for turbine exhaust because it provides good broadband attenuation. Still, the design can also be adjusted to target any low or high-frequency noise that may be a concern. Given this, it is common to see parallel baffles on the intake and exhaust of a gas turbine power island.

A typical silencer baffle consists of a frame for which the geometry is custom-designed to meet the project specifications. The absorptive properties of the silencer come from the insulation or infill system used within the baffle frame or cavity. The infill system is specifically designed to accommodate the temperatures of the silencer application. It includes protective layers to ensure a durable design when exposed to turbulent and violent exhaust flow, such as a simple cycle exhaust system.

Years ago, the original equipment manufacturer (OEM) would typically layer the needed materials into the silencer frame before enclosing the infill with the perforated facings. This layered approach has failure modes, which include:

  • Even with the infill compressed in the cavity (overfilled), the protective layers can be disrupted, exposing insulation and leading to an evacuation of the materials.
  • If a weld fails in the perforated sheet attachment, the protective layers can be severely disrupted, leaving a large opening for insulation to be evacuated.

What Are the Benefits of Acoustical Pillows?

Even if silencers are missing insulation, plant noise emissions may not be an issue. However, if material is ejected from your exhaust system, it can cause safety or environmental concerns. The best solution for high-performing silencer insulation is an acoustical pillow. Acoustic pillows are engineered to provide optimal acoustical absorption properties while deploying fibrous material protection schemes to ensure long-term service in volatile environments. Advantages include:

  • Acoustic pillows efficiently fill all zones of a baffle frame, eliminating voids and potential flanking paths for noise propagation.
  • Highly reinforced pillows can be used in exhaust sections with excessive turbulent flow or areas of high dynamic pressure pulsations.
  • After years of service, acoustic pillows are easily removed and replaced with newer, improved pillow construction methods.

What Are the Design Considerations for Acoustical Pillows?

Conventional acoustic pillows are used in high-temperature (700 °C/1,292 °F) environments, requiring temperature and fatigue-resistant materials to withstand the harsh conditions within gas turbine exhaust systems. Design considerations include:

  • The pillow’s core incorporates porous materials with excellent sound-absorbing properties, including basalt wool, mineral wool, ceramic fibers, and long-strand glass fibers.
  • Depending on silencer impinging flow characteristics, The core absorptive materials are protected with stainless steel wire meshes, silica or glass fiber mattings, and glass fiber cloths. All layers must have compatible airflow resistivity properties allowing soundwave penetration into the core fill material.
  • The geometry and density of the pillows are optimized to maximize sound absorption across a broad frequency spectrum, specifically to mitigate low-frequency combustion noise and higher-frequency jet mixing or blade interaction noise.

Final Thoughts About Acoustical Pillows

Switching to acoustical pillows for exhaust silencer insulation in gas turbine power generation can be a game-changer in noise reduction. While traditional methods have done their job well, acoustical pillows offer a giant leap in effectiveness, durability, and flexibility. By adopting these new solutions and recognizing their many advantages, power plant operators can manage noise reduction with greater assurance.

If you have concerns about your power plant’s noise footprint, the experts at SVI BREMCO can help. Contact us today to discuss your plant’s industrial noise reduction needs.